The present invention relates to an optical element at least a partial section of which has a light absorption property, a method of producing the same optical element, and an optical apparatus equipped with the optical element.
In an optical device such as light-source device, unwanted light out of use may generate stray light in the interior of the device and constitute a noise-component or the like. In the conventional optical device, generation of the stray light has been prevented by arrangement of optical elements having light absorption properties to absorb the unwanted light. Such elements previously known are constituted of members having a plate shape, a cone shape, or the like coated with a black coating.
As another example, black-coated plate having an optical aperture of circular or slit shape has been known as an optical element having light absorption property in at least a partial section. Such an optical element is used to constrict or shape a light flux (beam) to a circular shape, a slit shape or the like. Only to provide a beam-shaping function, a part of such an optical element may has a high reflectance except for a section where the light flux passes through. However, the light reflected from the part of high reflectance become stray light to constitute a noise component. Therefore, so as to prevent the generation of stray light, the reflectance is reduced by applying the black-coating at that part to provide light-absorption property.
An optical element provided recently has a micro-relief structure (micro-relief structure) constituted of numerous micro-protrusions (fine protrusions) formed on a surface of a silicon layer formed on a substrate such as a silica substrate (PCT International Publication for Patent Applications, WO2006/046502). This optical element is arranged such that the light is incident on the optical element from a side where the micro-relief structure is formed. According to this optical element, reflectance is reduced by the above-described micro-relief structure, thereby reducing reflection noise. Therefore, this optical element may be utilized, for example, as an optical mask that generates low reflection noise. In a method of producing an optical element disclosed in WO 2006/046502, a surface of a silicon layer is subjected to dry etching while depositing fine mask material on the surface of the silicon layer. As a result, a micro-relief structure constituted of randomly distributed numerous fine protrusions (micro-protrusions) is formed on the surface of the silicon layer.
Japanese Unexamined Patent Application, First Publication No. 2007-279084 discloses a source of laser light. There are various applications of laser light sources, for example, a light source of an exposure apparatus used in photolithography.